This invention relates to a coupling device such as a clutch device.
A clutch device which has a converter with a friction clutch comprising friction elements is known from German patent specification DE 198 38 443 C1. A first side of a piston can be acted on with an operating pressure, so that the friction elements are pressed together and torque transmission takes place. Cooling oil moreover flows through the friction elements. The friction clutch is supplied with cooling oil via a supply line and a return line. A valve which delivers a corresponding operating pressure when a control pressure is specified is provided for activating the friction clutch. The pressure of the cooling oil flow acts on a second side of the piston counter to the operating pressure. In order to compensate for reactions of pressure variations on the second side of the piston on the operating pressure, the pressure present outside the clutch is at the end of the coolant return line applied to the valve. The operating pressure is thus corrected to the pressure variations in the coolant return line.
It is an object of the invention to provide a clutch device in which the operating pressure correction takes place more accurately, that is as a function of the pressure present on the second side of the piston.
This object is achieved by a clutch device with the features claimed.
The clutch device according to the invention is designed as a hydraulic resistance cascade and is connected between coolant supply and coolant return lines of the friction elements of a clutch, a return pressure line branching off in the center of the hydraulic resistance cascade being connected to a valve. The hydraulic resistance cascade has two resistances via which a bypass oil flow flows from the coolant supply line to the coolant return line. An intermediate pressure is brought about between the hydraulic resistances. By varying the hydraulic resistances, the intermediate pressure can be influenced so that it corresponds to the coolant pressure acting at the piston. Advantageously, a pressure taken off between the hydraulic resistances is applied to the valve, so that activation of the friction elements which is free of reaction from the coolant pressure at the piston can take place via a control pressure. The hydraulic resistances can be constituted as restrictors, chokes, cross-sectional narrowings and/or hydraulic fluid lines of appropriate length and diameter, for example. The desired pressure drop can be set by means of the size of the cross-sectional narrowing and/or length and diameter of the portion of the bypass line before and after the take-off of the return pressure line, for example. The overall hydraulic resistance in the bypass line set by means of the restrictors determines the level of volume flow of the hydraulic fluid in the bypass line, or the volume flow through the friction elements.
In a development of the invention, the valve is a 3/3-way valve. The valve has a connection to the clutch, with a working pressure line and with a zero outlet which communicates with a transmission sump. In this connection, the valve can occupy three operating positions. In the first operating position, the working pressure is connected to the clutch, in the second operating position, the working pressure is separated from the clutch, and, in the third operating position, the clutch is connected to the zero outlet. By applying a control pressure on the one hand and a returned operating pressure on the other hand, an operating pressure present at the clutch and thus the torque transmitted via the friction elements can be adjusted with this valve.
In a further development of the invention, the valve has a slide which is arranged axially displaceably within a longitudinal bore of the housing. A 3/3-way valve can be brought about cost-effectively in the transmission by means of a slide.
In a further development of the invention, the slide has in an end region a slide bore with a piston arranged therein, which bore communicates with a peripheral groove of the slide. Operating pressure is present in the peripheral groove and, via a duct, is also present in the slide bore. The operating pressure is thus led back to an area on the slide corresponding in size to the piston area. By varying the piston area, a desired intensification, that is the ratio of control pressure to operating pressure, can be set.
In a further development of the invention, the slide has an annular surface which can be acted on with the pressure from the return pressure line. The return pressure gives rise to a force on the slide which advantageously ensures correction of the operating pressure as a function of the coolant pressure acting on the piston.
In a further development of the invention, a valve by means of which the pressure in the coolant supply line and/or the coolant return line can be limited to a maximum value is arranged in the coolant supply line and/or the coolant return line. The valve thus has the function of what is known as a pressure control valve. This effectively prevents the pressure in the coolant supply line and the coolant return line becoming too great and being able to cause damage to the clutch device. This risk exists in particular at very low temperatures and with rapid actuations of the clutch.
In a further development of the invention, a valve by means of which the pressure in the coolant supply line is reduced to a lubricating pressure level and limited to a maximum value is arranged in the coolant supply line. This valve therefore combines the functioning of what are known as a pressure-reducing valve and of a pressure control valve. One valve is thus sufficient for setting a defined lubricating pressure and protecting against excessive pressures in the lubricating system.
In a further development of the invention, the coolant return line of the friction elements and the hydraulic resistance cascade meet at a connection point, and the connection point in turn communicates with a supply of the transmission lubrication system, a cooler being connected before the supply of the transmission lubrication system. The entire coolant flow advantageously flows via the cooler in this arrangement, so that maximum cooling capacity of the friction elements and of the coolant is ensured. The coolant flow through the friction elements can be set by means of the hydraulic resistance cascade.
In a further development of the invention, a line to a cooler which is connected to a supply of a transmission lubrication system branches off from the coolant supply of the friction elements before the branching-off of the hydraulic resistance cascade. Part of the coolant flow flows via the friction elements into the transmission sump, and the other part flows via the cooler into the transmission lubrication system. This arrangement affords the advantage that no coolant which has already been contaminated with particles in the clutch enters the transmission lubrication system.
In a further development of the invention, a cooler is connected into the coolant supply line of the friction elements before the branching-off of the hydraulic resistance cascade and a line branching off which is connected to a supply of a transmission lubrication system is provided. The entire coolant flow flows into the cooler, part of the coolant flow then flows via the friction elements into the transmission sump, and the other part flows into the transmission lubrication system. This arrangement affords the advantage that the entire coolant flow flows via the cooler and no coolant which has already been contaminated with particles in the clutch enters the transmission lubrication system.
In a further development of the invention, the friction elements are components of a wet starting clutch. The device according to the invention makes it possible to automate a wet starting clutch so that engagement, disengagement and permanent slip operation can be performed with great comfort for the driver.
Further features and feature combinations emerge from the description and the drawings. Concrete illustrative embodiments of the invention are explained in greater detail in the description below and are shown in simplified form in the drawings.